The present invention relates to computer controlled printers and, more particularly, to such printers printing colored materials on the recording sheets to provide a color image.
The use of personal computers and, correspondingly, desk top printers controlled in part by such computers has increased very rapidly over the last several years. Many different printing technologies have been developed for these devices beyond that used in the impact printers initially performing in this role, including ink jet, thermal wax transfer and thermal diffusion, or dye sublimation, printing technologies.
These last technologies have been especially important in the growth of color printers, those having the capability of providing a colored image on a recording medium. The order of listing of these printing technologies above is typically the order of the quality of the results obtained in using them with ink jet technology generally providing the poorest quality of these technologies, and thermal diffusion giving the best. Unfortunately, the order of listing is also the order of cost with ink jet printers generally being cheapest and thermal diffusion printers being the costliest.
The desire for high quality in images recorded by such printers has led to those printers having often provided therein substantial computing capabilities in their own right to permit close control of electrical currents through the resistors in the thermal printhead which, in each supplying heat to the coloring material source to direct material therefrom onto the recording sheet, leads to each effectively providing a corresponding a color constituent of a pixel, on that sheet. In addition, extensive mechanical systems with expensive components such as high speed and high precision stepper motors, are usually used in such printers.
One possibility for reducing the cost of such printers is to have a significant fraction of the computing done by a computer controlling such a printer, as the capabilities of such computers have also grown substantially to permit such processing of printing data without too severely retarding the performance of the controlling computer in accomplishing its other purposes. However, the results of such computations in the controlling computer must be transmitted to the printer over the connecting cable which can take a relatively long time if the computer must be capable of transmitting for each printhead resistor any of all the possible intensities to be followed by that resistor, or any of all the possible patterns of intensities to be followed by groups of those resistors.
Another possibility to reduce cost is to always use the cheapest printing technology which will provide the needed quality in the resulting printed images. However, if quality needs differ from one printing task to another, purchase of sufficient different printers to provide the different printing technologies necessary will be expensive. Thus, there is a desire for less expensive color printers which do not lead to inordinately slow printing, or yield too poor a quality printing result, because of measures taken to reduce costs.